The present invention relates to the production and use of engineered phase-change particulate slurries, such as ice slurries, with high cooling capacity, fluidity, and stability to induce protective hypothermia through internal and external cooling.
It is well known that hypothermia can postpone damage to tissues caused by inadequate blood flow and oxygen deprivation. One important example of the potential protective properties of hypothermia is in the area of cardiac arrest. Sudden cardiac arrest is one of the leading causes of death in the United States, affecting about 1,000 people every day, most of them outside of a hospital setting. Despite widespread use of basic life support and advanced cardiac life support by paramedics, survival of cardiac arrest patients is usually less than 2-4%, in large part because cells of the brain and the heart begin to die within minutes following global ischemia, or inadequate blood flow.
The ability of these cells to survive severe ischemia can be significantly enhanced by transient hypothermia. However, rapid and significant cooling (within 10 minutes, and to a temperature of 34° C. or less) of a patient without blood flow in a pre-hospital setting has been unachievable.
External cooling methods have not been found effective in achieving the desired rates of cooling. Several studies by the applicants highlight the fact that current techniques of surface cooling alone are not effective for the rapid induction of hypothermia. In patients with normal circulation, the core cooling rates achievable with external cooling blankets and/or evaporative convection methods do not exceed 0.1° C./min. with rates on the order of 0.05° C./min. being more typical. This results in a cooling rate of less than 6° C. per hour, not rapid enough for protective use during cardiac arrest. Even with complete immersion of a human in an ice slush water bath (0° C.), achieving a nearly maximally effective surface heat transfer coefficient, the lack of blood flow during cardiac arrest prevents achieving the desired protective core cooling rates.
Accordingly, there is a need for a rapid and safe method of internally cooling the target zones—the heart, the brain, and other regions, which can be used in an out-of-hospital setting. The rapid induction of protective hypothermia using internal phase-change slurry cooling can have a significant impact on the rate of survival for patients suffering from a variety of conditions including, but not limited to, ischemia due to cardiac arrest, myocardial infarction, and stroke, hemorrhage, traumatic injury, and asphyxia.
There are significant theoretical advantages to inducing hypothermia in ischemic patients under field conditions, including the ability to cool ischemia-sensitive organs like the heart and brain more rapidly, and, therefore, reduce tissue injury caused by the sudden reperfusion of normothermic ischemic tissue.
The physics of thermal heat-transfer creates a formidable challenge to rapid cooling of a human with little or no circulation. This is particularly problematic since the brain and heart are the targets of the cooling process. External methods of cooling can lower the temperature of these oxygen-sensitive organs but only very slowly at rates of less than 0.05° C./min (only 3° C./hr). The difficulty is that without a pulse or adequate perfusion, there is very little transfer of heat from the deeper tissues to the superficial tissues. External cooling techniques (i.e. cooling blankets or even full ice-water immersion) during conditions of no or low blood flow only cools core organs via direct tissue thermal conduction. Unfortunately, the speed of cooling with these techniques is too slow to avoid a lethal outcome due to ischemic reperfusion injury to vital organs, including the heart and brain.